1. Field of the Invention
The present invention relates to an optical disc apparatus which makes recording of information on an optical disc and/or reproducing of information recorded on an optical disc possible, and in particular, the present invention relates to a structure of the optical disc apparatus which can perform recording of information and/or reproducing of information with reducing aberration.
2. Description of Related Art
An optical disc such as a compact disc (hereinafter referred to as a CD), or a digital versatile disc (hereinafter referred to as a DVD) has become popular. In addition, recently, to increase amount of information to be recorded on the optical disc, a study about high density recording on the optical disc is advanced, and for example, an optical disc which can record large capacity of information such as a HD-DVD which is high definition DVD or a Blu-ray disc (hereinafter referred to as a BD) has begun to be put to practical use. Further, in order to increase amount of information that can be recorded on the optical disc, development about a multilayer optical disc on which a plurality of recording layers are set up in a thickness direction of the optical disc, is performed actively.
To reproduce information on such optical disc and to record information on the optical disc are performed utilizing an optical disc apparatus. Because a plurality of kinds of optical discs are utilized recently as above described, development of an optical disc apparatus that can perform reproducing or recording of information for the plurality of kinds of optical discs is performed actively.
By the way, the optical disc such as a CD, a DVD, a BD, or the like, includes a transparent covering layer (protect layer) for protecting a recording layer having different thickness according to its kind. For example, the thickness for a CD is 1.2 mm, that for a DVD is 0.6 mm, and that for a BD is 0.1 mm. Because of this, in an optical disc apparatus which can perform reproducing and recording of information for such optical disc that has different thickness of transparent covering layer there is a case where a problem is caused by generation of spherical aberration when recording or reproducing of the optical disc is performed. Further, when recording or reproducing of the optical disc which has a plurality of recording layers is performed, there is a case where a problem is caused by generation of the spherical aberration because thickness of protect layer becomes different according to position of the recording layer. At this point, in this description, an intermediate layer between two recording layers of the multilayer optical disc is also presumed as the protect layer.
In this regard, heretofore a method or the like is proposed by that correction of the spherical aberration which causes problem in the optical disc apparatus is performed by arranging spherical aberration correcting means such as liquid crystal element, an expander lens, and the like in an optical system (for example, see JP-A-2005-158228). Further, in methods for the correction of the spherical aberration which have been performed heretofore, there is a method to perform the correction of the spherical aberration by moving a collimator lens that is arranged in an optical system of an optical disc apparatus along an optical axis direction depending on a kind of the optical disc which is subject to be recorded or reproduced, and arranging the-collimator lens most appropriately. In case of this method, it is effective because it has a merit that a structure of the optical system which is included in the optical disc apparatus can be simple and the like.
However, even in case where the method that the correction of the spherical aberration is performed by moving position of the collimator lens is utilized, there is a possibility that suppressing aberration which is generated in the optical system of the optical disc apparatus cannot be performed enough. In such a case, it causes a problem because quality of recording or reproducing by the optical disc apparatus is deteriorated.